GROSS ANATOMY OF FLOWERING PLANTS. XV 
others which have annual stems have biennial or perennial roots. 
In shrubs and trees the roots are of course perennial. Many root- 
lets, however, even in trees and shrubs die off in the autumn, and 
new ones are produced in the spring. 
Branching.—The branching of roots is usually very irregular. 
Where roots are branched, the main root is called the primary 
root, while its branches are secondary roots, In examining the 
branches of roots, notice that they spring from beneath the sur- 
face of the main root. In this they differ from the branches of 
stems. In stems the surface of the main stem is continuous with 
that of its branches, but in roots the surface is broken at the 
points where branches emerge. 
§ 38. Tue Lear. 
Position on the Stem.,—Leaves grow upon the stem in several 
ways. In some cases they are scattered (or alternate) (Fig. VII); 
Fig. VII. 
Fria. VII.—Scattered or alternate leaves. 
Fic. VILI.—Opposite leaves. 
in others they are opposite (Fig. VIII); in others again they are 
whorled (i.e., several occupy a circle around the stem). 
Parts.—Many leaves have three well-defined parts: 1. A broad 
or flattened part, the blade; 2. A leaf-stalk, upon which the blade 
